How to choose an email client: IMAP, privacy, platforms

An email client is the app you read and send mail with. A provider is the service that stores your mailbox and runs the servers. Choose the client by your devices, how many accounts it handles and whether its code is open. Choose the provider by where it hosts mail and how it encrypts it. Thunderbird is the main free desktop client in the email client ranking, and Proton Mail and Tuta lead the encrypted providers in the secure email ranking.

Clients and providers are separate choices

A client connects to your mail accounts and shows the mail on your device. A provider runs the servers that hold the mail. Thunderbird connects to many accounts but does not host mail itself. Proton Mail and Tuta are providers with their own apps. Mailbird is a client that combines Gmail, Outlook, Exchange and IMAP accounts in one workspace. Apple Mail is a client that comes with Apple devices.

The split matters for privacy. Changing the client does not change where your mail is stored. That is decided by the provider, so an encrypted provider is a separate decision from the app you read it in. Some encrypted providers limit how third-party clients can connect, so check that before you pick a client for them.

IMAP, SMTP and POP in plain terms

Account settings in most email clients use three protocols:

• IMAP keeps your mail on the server and syncs folders and read status across devices. Reading a message on your phone marks it as read on your laptop.
• SMTP sends outgoing mail from your client to the server, which passes it on to the recipient.
• POP3 is built around downloading mail to one device. It is less useful if you read mail on several devices.

A client that supports IMAP can usually connect to any mailbox that offers standard IMAP access. Mailbird's listing says it combines IMAP accounts with Gmail, Outlook and Exchange in one workspace. Some providers prefer their own apps or setup steps, so check the provider's setup page before you rely on a standard connection.

One inbox for several accounts

A unified inbox shows mail from several accounts in one list. Mailbird is built for that on Windows and Mac. eM Client syncs Gmail and Hotmail accounts and runs on Windows, macOS, Android and iOS. Spark runs one interface on iOS, Mac, Android and Windows, and its smart inbox sorts mail by importance.

With a unified inbox, check three things: that replies go out from the right address, that notifications show which account they came from, and that folders and labels from each provider still behave as you expect.

Privacy, calendars and AI features

Privacy in a client comes down to three questions: whether the code is open, whether the app adds tracking to the mail you send, and whether features send data to a service.

Thunderbird and Mailspring publish their source. Thunderbird's project says the app does not collect or store personal data unless you ask it to. Mailspring's read receipts and link tracking may not suit privacy-minded users, according to the ranking, so check whether you can turn them off before you choose it. Spark, eM Client, Mailbird and Apple Mail are closed source, so you rely on each vendor's statements.

AI features are a separate question. Spark's listing mentions an AI assistant, and eM Client sells AI features as add-ons. Check where those features process your mail before you turn them on.

Calendar and contacts are where clients differ most. Thunderbird includes a calendar and contacts on Windows, Linux and macOS. eM Client covers email, calendar and contacts on Windows, macOS, Android and iOS. Spark lists calendar support and integrations.

Some providers bundle these tools. Posteo includes email, calendar, address book and notes in one account. mailbox.org includes email, drive, calendar and video. Tuta offers end-to-end encrypted mail and calendar. Check that the contacts and calendar you need sync to every device you use.

Platform and price

The table compares six of the ranked clients. Prices are as listed in the ranking.

Client	Platforms	Phone app	Open source	Cost
Thunderbird	Windows, macOS, Linux	No	Yes, MPL-2.0	Free
Spark	iOS, macOS, Android, Windows	Yes	No	Free to start, Premium plan
Mailspring	macOS, Windows, Linux	No	Yes, GPL-3.0	Free download, Pro at $8 per month per its site
eM Client	Windows, macOS, Android, iOS	Yes	No	Free for home users, paid editions
Apple Mail	macOS, iOS	Yes	No	Free, included with Apple devices
Mailbird	Windows, macOS	No	No	Free download, paid plans

Apple Mail has no Windows or Android version, so it suits Apple-only households. Thunderbird has no phone app of its own, and its listing points to Thunderbird for Android as a separate project.

Encrypted providers

Provider encryption depends on the model, the hosting location and the features on each plan. The ranking groups them this way:

• Proton Mail offers end-to-end encryption between Proton users and describes its design as zero-access. It has a free plan and apps on every major platform. Its site describes the company as Swiss-based.
• Tuta encrypts mail and calendar end to end, uses post-quantum encryption and stores data on servers in Germany. Its free plan has 1 GB.
• Mailfence offers OpenPGP encryption in the browser, is protected by Belgian privacy law and has a free plan with 1 GB.
• Posteo starts at 1 euro a month with optional encryption of stored data. It has no free plan, and registration needs no personal details.
• Runbox is hosted in Oslo under Norwegian privacy law, supports browser PGP encryption and has a 30-day trial.
• mailbox.org uses German data centers certified to ISO 27001, with plans from 1 euro a month after a 30-day trial.

OpenPGP and end-to-end encryption between provider users are different tools. OpenPGP can encrypt mail to anyone who uses PGP, but it needs key management on your side. Provider-level encryption between users applies automatically when both people use the same provider, and it does not reach mail sent to outside services in the same way.

Our picks and what to do next

Clients, with the editorial score in brackets:

• Thunderbird (91.0): free and open source, with calendar and contacts on desktop.
• Spark (88.0): one app on iOS, Mac, Android and Windows, with a smart inbox.
• Mailspring (86.5): open-source desktop mail with send later and grammar checking.

Providers, with the editorial score in brackets:

• Proton Mail (92.0): zero-access encryption, a free plan and apps on every major platform.
• Tuta (90.0): encrypted mail and calendar on a free plan, with servers in Germany.
• Mailfence (86.5): OpenPGP in the browser and a free plan with 1 GB.

The ranking also includes StartMail (85.5), which is hosted in the Netherlands under Dutch and EU privacy law, offers PGP encryption in its web app and has no ads or tracking. It has no free plan beyond a 7-day trial that asks for payment details, and paid plans start at $4.99 a month.

If the mailbox itself must be encrypted, choose the provider first and then a client that connects to it. If the mailbox can stay where it is, choose a client by device coverage, calendar needs and whether you want open code. In both cases, test with your real account and an email with an attachment before you move everything across.